We have demonstrated antitumor properties of AmB for a number of specific tumors occurring in mice and humans, and that the basis for its unique antitumor action is an immunoadjuvant effect, and also an ability to increase the permeability of tumor cell membranes to antitumor agents. The latter has been exploited to overcome membrane-dependent resistance of tumors to antitumor agents in vitro and in vivo. In addition, we have been able to uncover a number of leads concerning the immunoadjuvanticity of AmB and its specificity for certain strains of mice. All of our evidence indicates that the unique properties of AmB, compared to other immunoadjuvants, may make it a more effective antitumor agent, and also may provide a means of studying host immune responses to tumors. On the basis of this work we now propose: 1. To explore the mechanism of action of AmB on cell membranes and define the basis for its unique properties as an immunoadjuvant and a permeabilizing agent. 2. To study the effectiveness of AmB against several tumors, the basis for its specificity as an immunoadjuvant and antitumor agent, and compare it to other immunoadjuvants. 3. To study the clinical usefulness of AmB as an antitumor agent, and further explore the possibility that the polyenes may provide a new kind of cancer therapy.